Refrigeration system



Nov. 1, 1949 E. w. z EARFoss, JR 2,487,012

REFRIGERATION SYSTEM Filed Jan. 8, 1946 INVENTOR.

Patented Nov. 1, 1949 REFRIGERATION SYSTEM Elmer W. Zeari'oss, Jr.,Philadelphia, Pa., assignor, by mesne assignments, to PhilcoCorporation,

Philadelphia, vania Pa., a corporation of Pennsyl- Appllcatlon January8, 1946, Serial No. 639,720

6 Claims. (Cl. 62-115) The present invention relates to refrigerationsystems and particularly to the control of refrigerant flow between thehigh pressure side and the low pressure side of a refrigeration systemof the capillary-tube restriction type.

As is commonly known in the art, systems of the general type abovereferred to are designed for optimum efficiency when operating underspecific conditions. For example, a system may be designed to operate atits best when the evaporator temperature is +10 F., and the roomtemperature is 90 F. In such a system, the capillary tube is soconstructed that the flow of refrigerant therethrough is exactlycontrolled (by the difference in pressure at the opposite ends of thetube) to prevent an excessive amount of gas from passing into theevaporator and to prevent an undue amount of liquid from accumulating inthe condenser, when the conditions are precisely as noted. However,these conditions are most unstable, due to the fact that the evaporatorand the condenser are subject, respectively, to variations in heat-loadand to variations in thermo-gradient. These variations in turn cause achange in pressure which deleteriously afiects the flow of refrigerantand accordingly lessens the efficiency of the system.

Thus, if the evaporator temperature is reduced, a correspondingreduction in evaporator pressure will follow-and therefore lessrefrigerant will be' pumped by the compressor so that an excessiveamount of gas, still containing heat of vaporization, will be forcedthrough the capillary and circulated throughout the system, accordinglyreducing its efliciency. Likewise, the efllciency of the system will beimpaired by the circulation of an excessive amount of heat laden gas, ifthe room temperature rises to a point where the condensing pressurebecomes so aflected that the refrigerant, discharged by the compressorinto the condenser, can not be fully condensed by the time it leaves thelatter to enter the capillary.

A rise in evaporator temperature or a drop in room temperature, will soaffect the condensation process that liquified refrigerant will beavailable in an amount greater than the amount which ;he capillary willallow to pass into the evaporator. Consequently the liquifiedrefrigerant will sack up into the condenser reducing its effective:ondensing surface and accordingly reducing the emciency of the system.

In ordinary capillary system, no provision is rnade to compensate fortemperature variations as Jutllned above, since, in such a system, the:apillary restriction is fixed and the flow of refrigerant is directlysubject to the differences in pressures betweenthe high side and lowside of the system. However, attempts have heretofore been made tocontrol the flow-retarding effect of a capillary tube by abstractingheat therefrom in response to variations in conditions which effectpressure changes within the refrigeration system. For that purpose, ithas been suggested to provide the system with an auxiliary capillarytube which forms apart of a liquid refrigerant receiving chamber, andwhich terminates with a portion arranged in heat exchange relation withthe discharging end of the main capillary tube. Such an arrangement mayfunction effectively so long as liquid refrigerant passes through theauxiliary capillary tube, but as soon as gas starts flowing through suchauxiliary tube, then the system operates in the same manner as it wouldoperate with a single capillary tube. Consequently such knownarrangements are subject to the same objections as hereinabove mentionedbecause in those arrangements the detrimental effects of a singlecapillary tube are merely transferred to a second capillary tube.

It is therefore, the primary object of this invention to overcome theabove mentioned objections and to assure optimum operation of a systemof the type referred to, by controlling the flow of refrigerant not onlythrough the main capillary tube but also through the auxiliary capillarytube.

It is another object of the invention to provide an arrangement wherebyheat may be abstracted from the auxiliary capillary tube, which itselfis utilized for the purpose of abstracting heat from the main capillarytube of the refrigeration system, so that the flow of refrigerantthrough the latter may be automatically varied in response totemperature-pressure changes in the system. The abstraction of heat fromthe auxiliary capillary tube results in cooling the refrigerant passingtherethrough and thus assures the presence of sufficient coolrefrigerant in an expanderportion of said tube for the purpose abovespecified.

Another and more specific object of the invention resides in theprovision of a novel arrangement and interrelationship of elementswithin a refrigerating system employing a main capillary tube and apilot" capillary tube, such arrangement and relationship of elementsresulting in greatly increasing the operational efl'iciency of thesystem for any given evaporator temperature and in ensuring maintenanceof optimum efiiciency of the system throughout a wide range ofevaporator temperatures.

Moreover, the invention is particularly characterized by the inclusionof an expander within a refrigerating system of the kind employing twocapillarly tubes, that is, a main capillary tube to tain amount of flashgas with the liquid refrigerant being supplied to the evaporator I. Inthe system illustrated in the drawing, the amount ofretard the flow ofrefrigerant from the condenser to the evaporator and an auxiliarlycapillary tube to control the flow retarding effect of the maincapillarly tube. This expander is associated with the two capillarytubes in such a manner that each are kept physically independent fromthe other so that the refrigerant circulating through said expander isthe sole influence on either capillary tube. Such an. arrangement makesit possible to obtain practically instantaneous control of therefrigerant flow through the main capillary tube.

These and other objects of the invention will be apparent from thefollowing description based upon the accompanying drawing, the singlefigure of which diagrammatically illustrates a possible embodiment of arefrigeration system constructed in accordance with this invention.

In the drawing, the invention has been shown as applied to refrigeratingapparatus of the compression type, but it is to be understood that theinvention. is applicable to other types of refrigcrating apparatus inwhich a volatile fluid may be evaporated upon absorbing heat andcondensed upon having heat abstracted therefrom.

As represented in the drawing, the system basically comprises anevaporator i and a condensing unit, the latter including a motorcompressor 2 and a condenser 3. The evaporator I: is associated with arefrigerator compartment 4 so that the-liquid refrigerant, as itevaporates in'said evaporator, may absorb heat from the air -\ivith'ir'isuch compartment to cool the same. The gas forming in the evaporator dueto the absorptiOllfOf heat during the vaporization process, is drawnthrough a suction line 5 into the compressor 2. There, the gas-iscompressed and discharged through a conduit 6 into the condenser 3 whichis flash gas is controlled to vary the restrictive effect of thecapillary tube so that the flow of refrigerant therethrough may beautomatically regulated in response to changes intemperaturepressureconditions within the system. For that purpose, aportion l6b of the capillary tube I6 is disposed for heat exchangerelation with an expander 20, the outlet end 2| of which discharges intothe evaporator inlet Ill. The inlet end 22 of the expander communicateswith the outlet end of an auxiliary or "pilot" capillary tube 23, theinlet end of which communicates with the liquid line at a point ahead ofand at a level slightly higher than the inlet of the main capillary tubeiii. In practice, the inlet end of the auxiliary capillary tube may besuitably connected with the top side of the filter l5, as indicated, at2 4, in the drawing. The auxiliary capillary tube 23 is so designed thatwhen the system is operating at maximum load, said tube will passapproximately one-third of the total amount of refrigerant supplied tothe evaporator, and therefore the restriction of the auxiliary capillarytube should be correspondingly higher than the restriction of the maincapillary tube i6.

Moreover, in accordance with the present invention, the auxiliarycapillary tube 23 is so constructed that the refrigerant passingtherethrough is placed in heat exchange relation with refrigerantemerging from said tube 23. For that purpose, said tube 23 has a port on23a disposed for heat exchanged relation with the expander 20, so thatthe refrigerant passing through the auxiliary capillary tube is in heatexchanged relation with the refrigerant which has passed through saidtube and discharged into the ex pander.

Operation of conventional systems at high evaporating pressure or at lowcon en in pressure, normally results in blocking the condenser.

exposed to room air so that heat may be abstractbecause the restrictionof the ordinary capillary ed from the compressed: refrigerant tocondense the same back to liquid state-From the condenser, the liquidrefrigerant flows to the evaporator through conduit means in the mannerto be hereso and the source of energy 8. A spring i 3 is pro vided to opose the force exerted by the bellows i0. and is adjustable by means ofa knob it so that the avera e evaporator temperature may be varied;within limits, at the will of the user.

In the svstem as shown in the drawing, liquid refri erant from theconden er 3 passes first throu h a fi ter i5 and then through a maincapillarlv tube I6. This capillary tube is connected with the outlet i?of the filter i 5 and discharges into the inlet i! of the eva orator I.As is customary. a portion Ilia of the capi lary tube It is arran ed inheat exchanged relation with a portion 5a of the suction conduit 5.

tube would prevent passage of the limiid at a rate commensurable withthe rate at which the liquid condenses, so that the liquid would thenback up into the condenser. However. this Working of +he condenser isovercome by the provision of the auxiliary capillary tube 23, becausethe liquid (which would ordinari y back up in the con denser), passesthrough said auxiliary capillary tube and through the expander Ml. Inpassing through the expander 20, the liquid removes flash gas and.therefore, subcools the refrigerant in port on l6b of the main capillarytube l6 and in a portion 23a of the auxiliary capillary tubr 23. therebyreducing the restrictive effect of both 30 tubes so that morerefrigerant passes into the evaporator when the system is operating athigh evaporating pressure due to a rise in evaporator temperature, orwhen the system is operating at low condensing pressure due to a drop inroom temperature. It is pointed out that when the svstem operates underthese conditions, the arran ement of portion 23a in heat exchangerelation with the expander, assures that liquid. will be discharged intothe expander in'quantit es sufflcient to provide adequate heat-exchan ewith the refrigerant passing through both the auxiliary and the maincapillary tubes. It will be understood that this feature results fromthe fact that refrigerant which emerges from the auxiliary capillarytube 23, expands upon entering the expander 20 and. thus, produces acooling effect on the refrigerant passing through portion 23a of theauxiliary capillary tube. Therefore, the amount of liquid refrigerantpassed by said tube is greater than the amount which the tube wouldnormally allow to pass.

Operation of conventional systems at low evaporating pressure or at highcondensing pressure normally results in gas blowing through to theevaporator. because then less refrigerant would be condensed andtherefore less liquid would be available at the entrance of the ordinarycapillary tube, so that the available liquid would soon be exhausted andan excessive amount of gas would pass through said capillary tube intothe evaporator. However, the passage of an excessive amount of gasthrough the main capillary' tube I6 is prevented by the provision of theauxiliary capillary tube 23, because the latter will then deliversaturated gaseous refrigerant, to the expander. Thus the refrigerantpassing through the expander will have but slight cooling effect on therefrigerant pass ng through portion I 6b of the main capillary tubeIGand through portion23a on auxiliary capillary tube 23 resulting nincreasing the restrictive effect of said main ca illary tube andtherefore preventing a rush of l quid therethrough and an exhaustion ofthe liquid at the entrance thereof. In this manner, the quantity ofliquid refri erant supplied to the .evaporator is substantially the sameas the qu ntity pumped by the compressor, so that the efli iency of thesystem is effectively maintained. The fact that the restrictive effectof the auxiliary capillary tube 23 is also controlled when the system isoperating at low evaporating pressure or at higlr con ensing pres ure.is an essent al factor in establishing and maintaining the operat o alef iciency of the svstem. Th s result is obtainable because, inaccordance with the invention. the flow of gaseous refrigerant. whichnormally would impair the operation of the system. is highly restrictedwhen the s stem is sub jected to low evaporat or to high condensingpressure conditions. This feature of the invention results from the factthat by lacing the refrigerant, passing through the auxiliary capillarvtube, in heat exchange relat on with refri erant emerg ng from sa dtube. it is possible to provide the system with a high restriction andto reduce the restrictive effect in response to chan es intemperature-pressure conditions within the s stem so that, for any givencondit on. the amount of gas discharged into the,

evaporator is efiectivelv decreased. This hi h restriction isparticularly advantageous in that it revents an excessive amount of gasfrom ent ring the evaporator when the system is o erating at lowevaporating pressure due to a d op in eva o tor tem erature. or when thes s em is operating at high condensing pressure due to a rise in roomtemperature. The gas, wh ch is held back due to the high restriction int e svstem, accumulates at the condenser and thus tends to increase thetemperature of the refrigerant and. therefore. to raise the condensingressure. As a result, the condensation process is re nlt a ed soonerthan if the gas were allowed to blow through the evaporator in the usualmanner. Thus, the proper balance between head and suction pressures isquickly restored so that loss in the efficiency of the system isminimized.

It is particularly pointed out that the overall efficiency of the systemdepends upon the perby placing the portion 23a thereof in heat exchangerelation with the beginning portion 20a of the expander 20 and byplacing the portion IGb of the main capillary tube in heat exchangerelation with the remaining portion 20b of said expander. In thismanner, the presence of liquid refrigerant within the expander in aquantity suflicient to effect heat exchange with the refrigerant passingthrough the main capillary tube is ensured, particularly because therefrigerant tube from the auxiliary capillary tube is effectively cooledat the beginning of the expander, the cool refrigerant beingsubsequently made available in the remaining portion of the expanderwith which the main capillary tube is in heat exchange relation.

It will be appreciated that the vaporation process which takes place inthe expander 20 results in subcoolin the refrigerant flowing throughboth capillary tubes. This vaporization process occurs particularl whenthe conditions within the system are such that the condenser would tendto block up with condensed refrigerant. When such conditions occur, thementioned vaporization process is initiated and continues until theliquid level in the condenser falls below the entrance to the auxiliarycapillary tube. In actuality this function of the system is periodic andvaries only in intensity to accommodate various load conditions;

From the foregoing, it will be understood that a refrigeration systemconstructed in accordance with the invention will adapt itself tovarying temperature-pressure conditions so that the proper flow ofrefrigerant, for any given condition, is automatically initiated andeffectively maintained throughout the system. Moreover, the system iscapable of quickly adjusting the refrigerant flow to a change in suctionpressure or in head pressure or both, when variations in evaporator orin room temperature, have affected such pressures. The quick adjustmentof the refrigerant flow results particularly from controlling therestrictive effect of the auxiliary or pilot capillary tube as well asthe restrictive effect of the main capillary tube. This characteristicfeature of the invention assures operation of the system at optimumefficiency over a wide temperature range and therefore minimizes thepossibilities of refrigeration failures, in the system, due to changesin temperature-pressure conditions.

It is to be understood that modifications may be made in theconstruction of the system without departing from the spirit of theinvention. Therefore, the invention is not limited to what is shown inthedrawing and described in the specification, but is subject only tosuch limitations as are imposed by the prior art or are particularlyindicated in the ap nded claims.

I claim:

1. In a refrigeration system, an evaporator, a condensing unit, and apair of conduits each conveying refrigerant from the condensing unit tothe evaporator, one of said conduits having an expander portion arrangedin heat exchange relation with another portion of said one conduit.

2. In a refrigeration system, an evaporator, a condensing unit, and apair of conduits each conveying refrigerant from the condensing unit tothe evaporator, one of said conduits having an expander portion arrangedin heat exchange relation with another portion of said one conduit, andwith a portion of the other of said conduits.

3. In a refrigeration system, an evaporator, a condensing unit, a mainand an auxiliary conduit each conveying refrigerant from the condensingunit to the evaporator, the auxiliary conduit having an expander portiondisposed for heat exchange with another portion of said auxiliaryconduit, and the main conduit having a portion arranged for heatexchange with said expander portion of the auxiliary conduit.

4. In a refrigeration system, an evaporator, a condensing unit, andmeans for conveying refrigerant from the condensing unit to theevaporator, said means including an expander and a pair of capillarytubes, one of said tubes communicating with the evaporator through theexpander and disposed for heat exchange relation with the latter, andthe other of said tubes communicating directly with the evaporator andalso disposed for heat exchange relation with the expander.

5. In a refrigeration system, an evaporator, a condensing unit, andmeans for conveying refrigerant from the condensing unit to theevaporator, said means including an expander 8. having its outletarranged for communication with the inlet of the evaporator, a capillarytube having its outlet arranged for communicationwith the inlet of theexpander and provided with a portion disposed for heat exchange relationwith the beginning portion of said expander, and another capillary tubehaving its outlet arranged for communication with the inlet of theevaporator and provided with a portion disposed for heat exchangerelation with the remaining portion of the expander.

6. In a refrigeration system, an evaporator, a condensing unit, and apair of conduits each adapted to pass and to restrict the flow ofrefrigerant from the condensing unit to'the evaporator, one of saidconduits terminating with an expander portion discharging into theevaporator and arranged in heat-exchange relationship with a portion ofeach conduit.

ELMER W. ZEARFOSS, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,183,343 Alsing Dec. 12, 19392,183,346 Buchanan Dec. 12, 1939 2,404,010 Urban July 16,1946

